Carburetor



May 23, '1939. E. scHlMANEK 2,159,294

CARBURETOR Filed Feb. 2, 1935 INVENTOR ATTORNEY Patented May 23, 1939 CARBURETOB Emil Schimanek, Mu'egyetem, ltudapest, Hungary Application February 2, 1935, Serial No. l44,611

In France February 5, 1934 1 claim.

The present invention relates to means for the automatic or at least partially automatic regulating of the mixture of fuel in motors at different altitudes. The invention refers only to car- 5 buretors with double carburation and with constant partial vacuum in the second Carburation space.

The invention utilizes the back pressure and the suction pressure of the air current in order to alter in carburetors, in which the fuel supply is eected at an always constant pressure-difference, this pressure-difference depending on the specific gravity of the air.

The invention makes use of the fact that for carburetors of the kind having a pre-carburation stage the supply-pressure or `feed pressure which sucks in the fuel, can be regulated in the precarburation space in which the first mixing of fuel and air takes place independently of the supply-pressurewhich prevails at the plac'e of the second carburation.

The invention contemplates that the back and suction pressure of the air flowing through the carburetor, which pressure is a function of the specific gravity of they air, is utilized not only mediately by means of being derived from the second mixing place but also immediately for supplying or conveying thefuel intothe first mixing place.

As is'known, the mixture in the carb of aircraft motors becomes richer as the height of the aeroplane increases. In order to establish the correct mixing proportions at all altitudes, various regulating devices have already beeny proposed which either work automatically or are controlled by the pilot. a

This invention utilises the dynamic eifect of the air current for the purpose of altering the difference of pressure that conveys the fuel into 40 the carburetor 'in dependence upon the specic gravity of the air.

' As is known, the mixture changes in consequence of the diminution of the specific gravity of the air in such a way that the quantity of air drawn in by the suction of the motor diminishes proportionally to the specific gravity of the air, while the quantity of fuel yonly decreases with the square root of this specific gravity. Consequently the mixture becomes richer when the specific gravity of the air decreases.

Let 'y be the weight of 1 4cubic metre of air, v`

the velocity of the air in metres per second,.and g the acceleration due to gravity in meters per second squared (9.81).

As isknown. ifa surface is exposed to a current of air the pressure upon the side of the surface facing the current is greater by 1u and the pressure upon its other side is less by L n 2 than the pressure in the neighbourhood of this surface.

Now if a tube is so arranged in a current of air that the air current blows vinto the opening of the tube, then the pressure in the interior of the tube is greater by 4 L. 1M than the pressure" beside the tube or outside the tube. If on the other hand the tube is so arranged that the current of air exerts a suc- .20

tionl eifect upon the aperture of the tube, then the pressurein the interior of the tube is less by than the pressure beside or outside the tube.

In both cases, if the velocity of the current of air does not change, the pressure in the interior of the tube will only vary with' the specific gravity ofthe air. If amotruns with thesame speed at ail altitudes without the adiustment of the throttle valve being altered. the motor always fills with the same volume of air. Consequently the pressure in the interior of a tube which is arranged in the current of air, as explained above, will only alter with the specific gravity of the air, since the speed of the air does not change.

'I'his invention utilises the fact lthat for carburetors of the kind in which the partial vacuum that sucks in the fuel is invariable and remains independent of the specific gravity of the air.

such a tube or the like which is exposed to the v In this way a complete regulation, or

renders it possible to influence the partial vacuum in the pre-carburation chamber independently of the constant partial vacuum in the main mixing chamber. In such carburetors as these the fuel first enters a chamber in which the partial vacuum is only a portion of that which prevails in the main mixing chamber, the quantity of air that flows into the pre-carburation charnber being only a portion of the total quantity of air. It therefore forms an emulsion with the fuel, which meets the main air in the mixing chamber with an invariable partial vacuum. The device according to the invention may then be such that the air supply to the pre-carburation chamber is so arranged that besides the dynamic effect of the air current the static partial vacuum in the pre-carburation chamber is also influenced. With the decrease in the specic gravity of the air, the partial vacuum in the precarburation chamber then also falls, whereby the enrichment of the mixture at a height ,is compensated for.

One example of construction of the invention is illustrated in the accompanying drawing which shows a.v regulating means according to thenvention on a carburetor with duplicate carburation in which the partial vacuum in the. main mixing chamber always remains unchanged.

As shown, air flows through a connecting piece `2 in the direction of the'arrow 3 into the carburetor and iiows from there in thedirection of the arrows into a mixing'chamber- I, where a second atomization takesplace. Part of this air flows through an aperture25 and tube 2I into a. pre-carburation chamber I8.- The fuel passes in the direction of the arrow I3 through a needle valve I5, which is controlled by a float I4, into a chamber I2, out of which it flows, through the cross section of the aperture I6 uncovered by the conical'needle I'I, into the chamber I8. In the chamber I8 an emulsion is formed, which passes through a passage 30 and an aperture I9 into the mixing chamber I. In the mixing chamber I the emulsion mixes with the main air of this chamber, and the'ultimate mixture flows through a connecting piece I provided with a throttle valve Il, tothe motor.

The chamber I8 is formed with a cylindrical extension 22 in which moves a disk 23 carried on the bottom of the needle II for braking or damping the movement of said needle;

The connection with the mixing chamber I is controlled by a piston 4, which is guided in a. cylindrical portion 5 of the casing, and assumes different positions according to the quantity of air drawn in by the suction of the motor, as a result of which it opens the aperture 'I leading to the mixing chamber I to a greater or less extent.

The difference of pressure between the chamber I and the space 2 underneath the piston 4, that is to say, the partial vacuum which draws the air by suction through the aperture I in the direction of the arr'ow 8, is always constant and independent of the specific gravity of the air.

The pressure of the chamber I is propagated through the aperture 9 into the space above the piston 4, so that the partial vacuum, whichsucks the air in the direction of the arrow 8, tends to raise the piston 4. This force or this tendency Vis counteracted by the weight of the piston 4,

constant vacuum in the chamber I determines a constant vacuum in the space I8, the vacuum `in the space I8, however, being less than the vacuum in the chamber I, because theI space I8 communicates by the aperture or apertures 25 with the space 2, in which the pressure is greater. In order to ensure complete regulation, it is necessary to regulate the aperture 25 correspondingly, and therefore to vary the vacuum in the chamber I8 to a corresponding extent. Therefor a lever 26 is provided witha conical closure piece 34, by the movement of which towards the aperture 25 the latter is closed to a greater or lesser extent, and therefore the partial vacuum in the space I8 can be accordingly altered. The vacuum in the space I8 diminishes of course with the enlargement of the aperture 25, and becomes greater when the aperture 25 is smaller. therefore the aperture 25 is completely closed, the pressure in the space I8 would be equal to the pressure in the space I. The air flowing in the neighbourhood of the aperture 25 exerts, however, upon the mouth ofthe aperture a suction effect which is proportional to the specific gravity of the air.v This suction effect and consequently also the vacuum in the space I8, is greater at the level of the ground .than at great altitudes. At greater altitudes the closure piece 34 must be moved further away'from the aperture .25. The adjusting of the closure piece 84 may be effected by any suitable controlling means within reach of the pilots hand.

'I'he air flowing in the direction of the arrow 3 enters the aperture 29 of the tube 83, and consequently the pressure in the space 28 above the surface of the fuel is greater at the ground level than at great altitudes. The fuel`is delivered by the difference of pressure between the space 28 and the space I8. At great altitudes the excess pressure in the space 28 diminishes, as also does the partial vacuum in the space I8. The pressure difference that delivers the fuel will therefore fall in consequence of these two effects. The quantity of fuel therefore diminishes in proportion as the altitude increases, and consequently the enrichment of the mixture in consequence of the decrease in the specific gravity of the air is compensated for.

'I'he utilisation ofthe dynamic eect of the air current is only limited by the air speeds which can be attained without considerable losses in cross sections in which the tubes for the utilization of this dynamic effect are located.

The more important the part played by the dynamic effect of the air current for the pressure difference that delivers the fuel, that is to say, the smaller this difference is without dynamic effect, the more complete will the above-described altitude regulation be. 'I'his is illustrated by the following example: f

Let it be assumed that the difference of pressure in the spaces 2 and I8 without dynamic effect is equivalent to a column of water I0 centimetres high, and letit be further assumed that in consequence of the dynamic effect at the ground level a raised pressure of centimetres (water column) in the space 28 and a partial vacuum of 15 centimetres (water column) in the space I8 arises.` Under these circumstances a. pressure difference of 30 centimetres (water column) will arise, which then, with the difference .of l0 centimetres, which is without dynamic ef-` fect, yields an aggregate difference of 40 centimetres (water column).

' At an altitude of 6000 metres the dynamic effect will produce a difference oi' 2 x 7,5:15 centimetres (Water column). The total difference of pressure which delivers the fuel will therefore amount to l0 l5=25 centimetres (water column).y The pressure difference delivering the fuel will therefore fall, at an altitude of 6000 metres, in the ratio of 25:40. Although this is not a complete regulation it will be sufllcient in practice for the satisfactory working of the motor at an altitude of 6000 metres.

For carburetors with invariable spraying nozzles the arrangement of a tube in the air current for regulating the suction vacuum is not applicable, since the vacuum which sucks in the fuel changes with the specific gravity of the air.

What I claim is:

In a carburetor for mixing fuel and air in two stages, a main air inlet, a fuel chamber, a fuel inlet for said fuel chamber, a rst stage mixing chamber, a passage leading from said fuel chamber to said lrst stage mixing chamber, a second stage mixing chamber in communication with the first stage chamber, an automatically operated valve for maintaining constant the partial vacuum in said second stage mixing chamber, a

passage leading from said main air inlet to said first stage mixing chamber for supplying air to said first stage mixing chamber, the entrance to said passage being arranged in a direction opposite to the air current in the main air inlet, a conically shaped. member in front of said entrance with its apex directed towards said air current so that the dynamic pressure of said air current in the main air inlet causes a suction effect on said entrance and means for adjusting said conical member relatively to said entrance in order to vary the partial vacuum in said first stage mixing chamber caused by said suction effect.

EMIL SCHIMANEK. 

